dart2js CPS: Small cleanup of the compilation pipeline.

pkg/compiler/lib/src/js_backend/codegen/unsugar.dart

 library dart2js.unsugar_cps;
 
 import '../../cps_ir/cps_ir_nodes.dart';
 
-import '../../cps_ir/optimizers.dart' show ParentVisitor;
+import '../../cps_ir/optimizers.dart' show ParentVisitor, Pass;
 import '../../constants/values.dart';
 import '../../elements/elements.dart';
 import '../../io/source_information.dart';
 import '../../js_backend/codegen/glue.dart';
 import '../../universe/selector.dart' show Selector;
 import '../../cps_ir/cps_ir_builder.dart' show ThisParameterLocal;
 
 class ExplicitReceiverParameterEntity implements Local {
   String get name => 'receiver';
   final ExecutableElement executableContext;
@@ skipping 12 matching lines @@
 
 
 /// Rewrites the initial CPS IR to make Dart semantics explicit and inserts
 /// special nodes that respect JavaScript behavior.
 ///
 /// Performs the following rewrites:
 ///  - Add interceptors at call sites that use interceptor calling convention.
 ///  - Add explicit receiver argument for methods that are called in interceptor
 ///    calling convention.
 ///  - Convert two-parameter exception handlers to one-parameter ones.
-class UnsugarVisitor extends RecursiveVisitor {
+class UnsugarVisitor extends RecursiveVisitor implements Pass {
   Glue _glue;
   ParentVisitor _parentVisitor = new ParentVisitor();
 
   Parameter thisParameter;
   Parameter explicitReceiverParameter;
 
   // In a catch block, rethrow implicitly throws the block's exception
   // parameter.  This is the exception parameter when nested in a catch
   // block and null otherwise.
   Parameter _exceptionParameter = null;
 
   UnsugarVisitor(this._glue);
 
+  String get passName => 'Unsugaring';
+
   bool methodUsesReceiverArgument(FunctionElement function) {
     assert(_glue.isInterceptedMethod(function));
     ClassElement clazz = function.enclosingClass.declaration;
     return _glue.isInterceptorClass(clazz) ||
            _glue.isUsedAsMixin(clazz);
   }
 
   void rewrite(FunctionDefinition function) {
     thisParameter = function.thisParameter;
     bool inInterceptedMethod = _glue.isInterceptedMethod(function.element);
@@ skipping 213 matching lines @@
       insertLetPrim(newReceiver, contBinding);
     }
     node.arguments.insert(0, node.receiver);
     node.receiver = new Reference<Primitive>(newReceiver);
   }
 
   processInterceptor(Interceptor node) {
     _glue.registerSpecializedGetInterceptor(node.interceptedClasses);
   }
 }